var deduped = [ 1, 1, 'a', 'a' ].filter(function (el, i, arr) {
    return arr.indexOf(el) === i;
});

console.log(deduped); // [ 1, 'a' ]

var deduped = [ 1, 1, 'a', 'a' ].filter( (el, i, arr) => arr.indexOf(el) === i);

console.log(deduped); // [ 1, 'a' ]

var deduped = Array.from( new Set([ 1, 1, 'a', 'a' ]) );

console.log(deduped); // [ 1, 'a' ]